A number of methods and devices aimed at combating the above effects are used in drilling.
For example, a prior art bottom-hole feeding mechanism is formed as a part of bottom-hole assembly comprising a drilling string, a drill bit, a bottom-hole motor and a telescopic system (Patent of the Russian Federation No. 2164582, E21B7/08, published on Mar. 27, 2001).
The disadvantages of the prior art solution include complexity and lack of drill bit load adjustment during drilling.
The prior art for the present invention is a bottom-hole feeding mechanism comprising a cylinder coupled with the drilling string, a piston received therein and a hollow spindle coupled therewith and coupled with a piston engaged with the inner surface of the cylinder having a hollow rod arranged along the cylinder axis. The hollow rod, the piston and the cylinder form a closed chamber containing a throttle with a parallel hydraulic channel having a spring-loaded check valve. The outer diameter of the rod differs from the outer diameter of the piston, and the connection between the spindle and the cylinder is formed by a splined non-locking screw pair (Patent of the Russian Federation No. 2439282, E21B19/08, published on Jan. 10, 2012, BM No. 1 and the Eurasian Patent No. 019323).
The prior art technical solution has the following disadvantages.
The device is not effective enough at damping axial vibrations arising during operation of the bottom-hole motor and the drill bit. Indeed, the arrangement in which the connection between the spindle and the cylinder is formed by a splined non-locking screw pair allows transferring both rotational and axial load to the splined pair, but limits device sensitivity to changes in longitudinal vibration acting on the screw spindle. It has been established that a splined pair formed with a screw surface inhibits the process of transferring axial load from the source of longitudinal vibration to the piston due to strong frictional forces between splines.
As a result, a portion of axial vibration energy and a portion of energy of single strong axial impacts arising in bottom-hole assembly elements below the device during drilling due to frictional forces in the splined screw pair are not transferred to the device piston for subsequent damping in the closed chamber throttle, but are rather transferred directly to the cylinder and further to the drilling string by frictional forces in the splined screw pair. It is apparent that said portion of axial vibration energy is not dampened in the prior art device.
Further, the device is ineffective at damping significant impact loads, both axial and rotational. Indeed, when drilling horizontal borehole portions and when axial load transfer control is difficult, the force of axial and rotational impacts can reach significant values substantially exceeding feed force achieved by the device, thus leading to the spindle being completely recessed into the cylinder. The above behavior was encountered during use of prototype in borehole conditions.
A further disadvantage of the prior art device is that significant frictional forces in the splined screw pair significantly decrease the feed force achieved by the device, thus decreasing efficiency thereof.
A technical solution that also allows damping of rotational and axial vibration due to the fact that the splined connection is formed as a splined surface is known in the art (US Patent Application No. 20080202816, Torque Converter for Use When Drilling with a Rotating Drill Bit).
However, US 20080202816 cannot generate additional axial feed force for loading the drill bit, which is a significant factor in drilling, e.g., horizontal boreholes, in which case providing load to the drill bit is inhibited due to strong frictional forces. In drilling, when calculating the load on a hydraulic jar, the said force is referred to as “pump open force”, and in oil extraction using plunger sucker-rod pumps, it is referred to as “Lubinski effect”. The load component is often disregarded, but it can be significant values and, therefore, should be considered while operating the disclosed device. The nature of said force is described in: 1) “The Effect of excessive pressure in pipes on operation of hydraulic jars”, S. Yu. Vagapov, G. G. Ishbaev, “Drilling and Oil”, No. 12, 2008; 2) “Buckling of tubing in pumping wells, its effects and means for controlling it”, Arthur Lubinski, K. A. Blenkarn, SPE-672-G Document ID, Society Petroleum Engineering, 1957.
Furthermore, the prior art technical solution lacks a closed hydraulic cavity with a throttle and a check valve that would provide throttling and dissipation of energy of both axial and rotational impacts.
On the other hand, the solution with only one spindle fails to effectively dampen axial vibration caused by strong frictional forces in the splined screw connection.
Further, a technical solution allowing to use the pump open force (POF) for providing axial load to the drill bit is known in the art (Dailey CBC-THRUSTER Tool, Weatherford Drilling and Intervention). However, the prior art device cannot provide feedback between axial load to the drill bit and rotational torque due to the use of a splined connection with axial (and not screw) splines.